There are two ways to allow / restrict system login to specific user groups only. The simplest method is to use a PAM module called pam_listfile.so. Another option is to use login access control table. Locking down system login access is very important task if you need a secure system. The system administrator is free [...]
The idea is very simple you want to limit who can use sshd based on a list of users. The text file contains a list of users that may not log in (or allowed to log in) using the SSH server. This is used for improving security. PAM (Pluggable authentication modules) allows you to define [...]
Recently I was asked to control access to couple of services based upon day and time. For example ftp server should be only available from Monday to Friday between 9 AM to 6 PM only. It is true that many services and daemons have in built facility for day and time based access control.